Electrophotographic processes such as that used in printers, copiers, and fax machines produce hardcopy images on a print media such as paper through precise deposition of toner onto the print media. The toner is applied by the print mechanism to correspond to the desired text or image to be produced. Such toner is then permanently affixed to the media by a fuser, which heats the toner such that it melts and bonds to the print media.
Typically the fuser comprises at least two contiguous rollers, a hot roller and a backup roller. The media is transported to the print mechanism and passes between the contiguous rollers, such that fuser hot roller heats the media to melt and fuse the toner to the print media.
As the toner melts, it becomes tacky and has a tendency to adhere to the fuser hot roller. Over time, toner accumulates on the hot roller, and eventually on the backup roller, causing degradation of the image quality on the print media.
Application of a lubricating substance to the fuser hot roller serves to weaken the bond between the toner and the hot roller and prevents accumulation of toner on the hot roller, and also serves to smooth the toner surface. Silicone oil is one such lubricating substance which has effective toner repelling properties. Alternatively, such oil can be applied to the backup roller, and then transferred to the fuser hot roller due to rotational engagement of the backup roller with the fuser hot roller.
There are a variety of prior art oil delivery systems to apply silicone oil to the fuser hot roller. Oil webs, oil wicking systems, and oil delivery rolls have been employed to provide a controlled supply of oil to the hot roller. Such prior art mechanisms, however, increase the complexity of the system by adding moving parts, and increase maintenance because of the need to maintain a supply of silicone oil. Further, as such oil delivery systems tend to promote a continuous oil flow, an idle period between printing cycles can result in a surge of oil, called an oil dump, during a successive print phase. Such oil dumps can compromise the finished print quality, and further can damage the printer if excess oil leaks onto other components.
One prior art oil delivery system is shown in FIG. 1, in which an oil web 10 extends from a web supply roll 14 to a web take-up roll 12. The web is generally a fabric material of one or more layers and is held in contact with the fuser hot roller 18 by one or more biasing rollers 16. Oil delivery is controlled by indexing the web 10 by controlled rotation of the take-up and supply rolls 12 and 14. While effective at delivering oil, such an oil delivery system generally increases the number of moving parts, affecting cost and maintenance.
Another prior art oil delivery system is shown in FIG. 2, which utilizes a wicking element 20 biased against the fuser hot roller 18 by a spring loaded or other biasing member 22 mounted on a support 23, or otherwise disposed in contact with the fuser hot roller. The wicking element is a piece of fibrous textile or mesh material adapted to transport silicone oil through capillary action. As the wicking element extends from an oil reservoir 24 to the hot roller 18, the wicking element is therefore adapted to deliver silicone oil along the length of the fuser hot roller 18. Such a system, however, tends to be prone to oil dumps due to the capillary characteristic of the wicking element material, and further requires a separate oil reservoir 24 to be maintained.
FIGS. 3a and 3b show prior art oil delivery rolls. Such rolls utilize an outer metering layer wrapped around an oil containing center. FIG. 3a shows a web wrapped roll 34, which includes an oil saturated wrapping 30 such as a temperature resistant paper or non-woven material around a support shaft 36. An outer metering layer 38, such as felt or a metering membrane, is wrapped around the oil saturated wrapping to limit the flow of oil brought to the surface by the capillary action of the oil saturated wrapping. FIG. 3b shows a tank-type oil roll which uses a hollow support shaft 44 as an oil reservoir. The hollow support shaft has oil delivery holes 46 along the length for delivering oil to a metering material 42, such as rolled fabric, which is wrapped around the hollow support shaft 44. Each of these oil delivery rolls shown in FIGS. 3a and 3b rotationally engage the fuser hot roller for the purpose of applying oil. Such an oil delivery roll, however, requires periodic replenishment of the oil reservoir and can also result in oil dumps if the oil delivery roll remains in contact with the fuser hot roller during idle periods.
An oil impregnated rubber roller for an electrophotographic printer fuser allows silicone oil to secrete from the rubber roller onto the fuser hot roller to prevent toner from adhering to the fuser hot roller. Such an oil impregnated roller provides oil delivery to the fuser hot roller without the need for a separate oil reservoir and delivery system. The oil impregnated roller decreases the potential for large surges of oil onto the print media, while continuing to provide a controlled delivery of oil to the fuser hot roller.
Such an oil impregnated roller is comprised of a cylindrically shaped silicone rubber roller disposed around a rotatable shaft. The silicone oil is impregnated into the silicone rubber roller during the rubber manufacturing process, rather than saturated or injected by a secondary process following manufacturing.
The secretion rate of the oil from the oil impregnated roller to the fuser hot roller is affected primarily by the viscosity of the silicone oil and the rotational speed of the rollers. The viscosity of the oil tends to decrease with increased temperature. Accordingly, the silicone oil impregnated in the roller is selected to be of a viscosity which secretes at a desired flow rate at the operating temperature of the fuser hot roller. A greater flow rate can be achieved by decreasing the viscosity of the silicone oil selected. Further, as the fuser hot roller generally cools during idle periods, the oil viscosity increases and therefore flows less freely; thus the oil impregnated roller can remain in contact with the fuser hot roller for extended idle periods without increasing the potential for oil dumps.
As the secretion rate of the silicone oil is most affected by the viscosity of the oil, a larger quantity of impregnated silicone oil does not substantially increase the flow of oil. Therefore, the flow rate tends to remain consistent regardless of the quantity of oil remaining impregnated in the roller. Accordingly, a large quantity of oil can be impregnated in the silicone rubber, thereby increasing longevity of the oil impregnated roller without affecting the flow rate or increasing the potential for oil dumps.
It would be beneficial, therefore, to develop an oil delivery system which reduces the number and complexity of moving parts, avoids the maintenance of an oil reservoir, and which avoids the tendency for oil dumps, while still providing a carefully metered supply of oil to the fuser hot roller.
An oil secreting roller comprised of a plurality of layers, one of which is comprised of a homogenous, oil secreting substance. A metering membrane layer, such as expanded polytetrafluorethylene (PTFE), felt, or paper, is wrapped around the cylindrical roller element to further limit and control the amount of oil exuded. Also, the oil secreting cylindrical roller element may be disposed around an inner silicone rubber layer or other inner buffer layer to minimize swelling, since the oil secreting portion may have a tendency to swell, depending on the type of oil used, the type of rubber used, or the operating temperature. Finally, a barrier layer such as VITON(copyright) may be provided between the inner buffer layer and the oil secreting cylindrical roller element to minimize diffusion of the silicone oil into the inner buffer layer.
A cleaning element such as a cleaner roller, wiper, web, or scraper can be provided in contact with the hot roller or a roller engaged directly or indirectly therewith to remove excess toner, dust or other particles which may accumulate on the roller surfaces.